1. Field of the Invention
This invention relates generally to a manufacturing process of thin film magnetic head sliders, and more specifically to a manufacturing process of thin film magnetic head sliders having high reliability and improved manufacturing yields.
2. Description of the Related Art
As a magnetic head for use in recording and reading information on a magnetic disk, a thin film magnetic head formed by laminating a thin film on the trailing side surface of a slider made of a non-magnetic material, such as alumina titanium carbide is commonly used. A known manufacturing method of a slider having a thin film magnetic head, that is, a thin film magnetic head slider, is such that a thin film magnetic head slider is obtained by forming a few hundreds of thin film magnetic head elements (electromagnetic conversion elements) on an end face, that is a front side surface, of a disk-shaped substrate wafer, with the thin film deposition technologies, slicing the substrate wafer into rectangular blocks (row bars) in such a manner that each of row bars includes about ten thin film magnetic head elements arranged in a line on the row bar surface. The row bars are then machined to have a given gap depth and an air bearing surface and cut into each slider, as disclosed in JPA3-295017.
According to JPA3-295017, 3 inch-dia., 4.0 to 4.6 mm-thick substrate wafers are used to obtain 3.2 mm-long magnetic head sliders. When slicing a substrate wafer, on an end face, that is, a front side surface of which hundreds of thin film magnetic head elements have been formed, into row bars, a large number of grooves are provided on the front side surface of the substrate wafer by scribing the row bar from the front side surface along the width of the row bar with a small thickness of the other end face, that is, the back side surface of the substrate wafer, left uncut so as to prevent the row bars from separating apart. After that, grinding is performed from the back side surface of the substrate wafer to reach the aforementioned grooves, and the wafer is separated into row bars.
As a magnetoresistive thin film magnetic head which combines a magnetoresistive reproducing element and an inductive recording element has been put into practical applications, recording density has been remarkably improved. With increases in recording density, the size of the thin film magnetic head slider has also been rapidly reduced; the length of the slider has been reduced from 3.2 mm (70%) to 2.0 mm (50%), to 1.25 mm (30%), and even to 1 mm (25%) or less. The percent figures in parentheses are designations used in IDEMA standards. The thin film magnetic head slider has been reduced substantially not only in length but in width and thickness.
With decreases in the length of the slider, the thickness of the substrate wafer used has also been reduced. In JPA3-295017, a substrate wafer of 4.0 to 4.6 mm in thickness was used to fabricate a 3.2-mm (70%) slider, whereas a 2.0 mm-thick substrate wafer was used to fabricate a 1.25-mm (30%) slider in JPA8-241514. It is quite natural in terms of improved material yields to use a thinner substrate wafer to fabricate a shorter slider.
The thin film deposition process for forming thin film magnetic head elements includes photolithography, sputtering, ion milling, plating, etc. Since these treatments are usually carried out on each substrate wafer, man-hours for a substrate wafer remain almost the same, independent of the size of wafer. Increasing the size of a substrate wafer, therefore, offers an advantage of increasing the number of thin film magnetic heads produced from a single substrate wafer. When a substrate wafer of 6 inches in diameter is used, for example, the area of the wafer from which thin film magnetic heads can be manufactured is quadrupled in a simple calculation. In other words, about four times as many as thin film magnetic heads can be manufactured with almost the same man-hours. Thus, the size of the thin film wafer used in the manufacture of thin film magnetic heads has been increased from the conventional 3 inches to 4 inches, to 5 inches, and then to 6 inches. From a substrate wafer of 6 inches in diameter, for example, 7,000 to 9,000 pieces of 50% sliders or 15,000 to 20,000 pieces of 30% sliders can be manufactured.
In this way, the larger the diameter of substrate wafers, the thinner the become in thickness. As substrate wafers become larger in diameter and thinner in thickness, the substrates tend to be bent materially, leading to deterioration in levelness, posing a big obstacle in the formation of thin film magnetic head elements. The bending of the substrate may change the exposure focal distance of the photoresist, and change the local shape of the photoresist. When a mechanical grinding and/or lapping process is included in the manufacturing process of thin film magnetic head elements, the bending of the substrate may lower grinding and/or lapping accuracy.
Worsened grinding and/or lapping accuracy poses no problem in fabricating sliders, using a substrate wafer of about 3 inches in diameter. Fabricating 3.2 mm-long sliders using a 3 inch-dia. substrate wafer, as in JPA3-295017, poses no problem. In JPA8-241514, thin film wafers as thin as 2.0 mm are used, and their diameter is not shown. But, the diameter of the substrate wafer used is considered to be 3 inches judging from the fact that the length of row bars as the intermediate product is 50 mm. Since the bending of the substrate wafer does not cause any problem so long as a 3 inch-dia. substrate wafer is used, JPA8-241514 discusses only countermeasures for the bending of row bars caused after they were subjected to subsequent processing.
Thin film magnetic head elements are usually manufactured in thousands to ten thousands at a time by sequentially laminating thin films on a substrate wafer using the thin film deposition process. For this reason, even when part of the magnetic head elements on a single substrate wafer become defective, the manufacturing process is continued all the way through the final stage without removing the defective part. The defective part of the thin film magnetic heads is removed only after individual thin film magnetic head sliders have been finished by cutting row bars. To facilitate identifying individual sliders, including defective sliders, a marker representing the identification number of each sliders is provided on the substrate surface on which the element is formed, that is, the trailing side surface of slider. On the end surface opposite to the element forming surface of the slider, i.e. the leading side surface, normally provided are wafer and manufacturing lot numbers using the laser marking method. Since the manufacturing history and the location on the substrate wafer of each thin film magnetic head slider can be identified with these laser marks and the identification number on the element forming surface, the defective sliders can be easily removed, and the cause of defects can be easily detected and analyzed.
According to the process disclosed in JPA3-295017, row bars are fabricated by scribing many grooves in advance on a substrate wafer on which thin film magnetic head elements were formed, and grinding and/or lapping the back side surface. In the process disclosed in JPA8-241514, row bars having a slightly greater width than the length of the slider are fabricated by cutting a substrate wafer on which thin film magnetic head elements were formed, and then the surface of the row bar opposite to the surface on which the thin film magnetic heads were formed, that is, the leading surface of slider, is cut for removal. In these prior-art processes, wafer and manufacturing lot numbers and other markers have had to be provided on the leading side surface of slider, that is, the surface of slider opposite to the surface on which the elements were formed only after the substrate wafer containing thin film magnetic head elements has been fabricated into row bars, or into sliders. For this reason, much care has been required to control manufacturing lots so as to prevent manufacturing lots from being confused in providing markers with laser marking. Furthermore, laser marking in the state of row bars or sliders has involved a great amount of man-hours in handling them.